Response of plants to calcium concentration in solution culture

Calcium concentrations required in solution for growth of 30 grasses, cereals, legumes, and herbs were defined for a wide range of concentrations which were maintained constant in Bowing culture solutions of pH 5.7. Contrary to published results obtained with standard nutrient culture techniques, some legumes and herbs grew much better at low concentrations of calcium (2.5 and 10µM ) than many Gramineae. The minimal concentration required to produce maximum growth of plants and eliminate calcium deficiency symptoms varied widely (2.5–1000 µM) within each group; it varied over the same range for Gramineae as for legumes and herbs. At 100 µM all plants grew well without symptoms of calcium deficiency. Increasing the concentration to 1000 µM increased growth in only a few species. At concentrations < l µM , severe deficiency symptoms developed on the tops of all species. The growth of legumes and herbs was more quickly and more severely affected than that of Gramineae. The roots of many legumes and herbs also degenerated rapidly. In the same solutions the roots of all Gramineae appeared healthy for some time. However, the advantage of Gramineae in these solutions was transitory, since the high relative growth rate in their early growth stages fell rapidly. It is suggested that distinct processes dominate the plants' behaviour at each range of calcium concentrations. At extremely low concentrations (< l µM ) , to which legumes and herbs are more sensitive than Gramineae, the dominant process may involve ion exchange equilibria between calcium in the environment and in the cell walls or membranes. At higher concentrations (2.5–1000 µM), to which Gramineae are as sensitive as legumes and herbs, processes of absorption of calcium from solution and translocation to plant tops are probably dominant.